System and method for scalable and space efficient hardening of a fixed sized hash table over an unreliable tier

ABSTRACT

A method, computer program product, and computer system for storing data in a bucket of a plurality of buckets. A spare bucket may be reserved in the plurality of buckets. A copy of the data may be stored in the spare bucket. A pointer to the data in the bucket and a pointer to the copy of the data in the spare bucket may be updated based upon, at least in part, storing the data in the bucket and storing the copy of the data in the spare bucket.

BACKGROUND

Some storage systems may need to harden data structures intonon-volatile memory block devices (e.g., HHD and SSD). Generally,storage systems for a simple read-modify-write operation are non-atomic.A reason common in storage systems for a simple read-modify-writeoperation to be non-atomic is RAID over multiple disks (each device mayonly provide atomicity in its own native block size). However,generally, the read-modify-write operation must be atomic to guaranteeconsistency in failure condition. This issue is traditionally solved byexcessive journal implementations.

BRIEF SUMMARY OF DISCLOSURE

In one example implementation, a method, performed by one or morecomputing devices, may include but is not limited to storing data in abucket of a plurality of buckets. A spare bucket may be reserved in theplurality of buckets. A copy of the data may be stored in the sparebucket. A pointer to the data in the bucket and a pointer to the copy ofthe data in the spare bucket may be updated based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.

One or more of the following example features may be included. The sparebucket may be a next slot from the bucket. Updating the pointer to thecopy of the data in the spare bucket may include pointing to the bucketstoring the data. The plurality of buckets may be updated in aconsecutive-cyclic manner. The plurality of buckets may be dividedbetween a fixed number of domains. Each domain of the fixed number ofdomains may be an instance of an independent logical tier. Each domainof the fixed number of domains may include its own header and sparemetadata member.

In another example implementation, a computing system may include one ormore processors and one or more memories configured to performoperations that may include but are not limited to storing data in abucket of a plurality of buckets. A spare bucket may be reserved in theplurality of buckets. A copy of the data may be stored in the sparebucket. A pointer to the data in the bucket and a pointer to the copy ofthe data in the spare bucket may be updated based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.

One or more of the following example features may be included. The sparebucket may be a next slot from the bucket. Updating the pointer to thecopy of the data in the spare bucket may include pointing to the bucketstoring the data. The plurality of buckets may be updated in aconsecutive-cyclic manner. The plurality of buckets may be dividedbetween a fixed number of domains. Each domain of the fixed number ofdomains may be an instance of an independent logical tier. Each domainof the fixed number of domains may include its own header and sparemetadata member.

In another example implementation, a computer program product may resideon a computer readable storage medium having a plurality of instructionsstored thereon which, when executed across one or more processors, maycause at least a portion of the one or more processors to performoperations that may include but are not limited to storing data in abucket of a plurality of buckets. A spare bucket may be reserved in theplurality of buckets. A copy of the data may be stored in the sparebucket. A pointer to the data in the bucket and a pointer to the copy ofthe data in the spare bucket may be updated based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.

One or more of the following example features may be included. The sparebucket may be a next slot from the bucket. Updating the pointer to thecopy of the data in the spare bucket may include pointing to the bucketstoring the data. The plurality of buckets may be updated in aconsecutive-cyclic manner. The plurality of buckets may be dividedbetween a fixed number of domains. Each domain of the fixed number ofdomains may be an instance of an independent logical tier. Each domainof the fixed number of domains may include its own header and sparemetadata member.

The details of one or more example implementations are set forth in theaccompanying drawings and the description below. Other possible examplefeatures and/or possible example advantages will become apparent fromthe description, the drawings, and the claims. Some implementations maynot have those possible example features and/or possible exampleadvantages, and such possible example features and/or possible exampleadvantages may not necessarily be required of some implementations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example diagrammatic view of a bucket process coupled to anexample distributed computing network according to one or more exampleimplementations of the disclosure;

FIG. 2 is an example diagrammatic view of a storage system of FIG. 1according to one or more example implementations of the disclosure;

FIG. 3 is an example diagrammatic view of a storage target of FIG. 1according to one or more example implementations of the disclosure; and

FIG. 4 is an example flowchart of a bucket process according to one ormore example implementations of the disclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION System Overview

In some implementations, the present disclosure may be embodied as amethod, system, or computer program product. Accordingly, in someimplementations, the present disclosure may take the form of an entirelyhardware implementation, an entirely software implementation (includingfirmware, resident software, micro-code, etc.) or an implementationcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore, insome implementations, the present disclosure may take the form of acomputer program product on a computer-usable storage medium havingcomputer-usable program code embodied in the medium.

In some implementations, any suitable computer usable or computerreadable medium (or media) may be utilized. The computer readable mediummay be a computer readable signal medium or a computer readable storagemedium. The computer-usable, or computer-readable, storage medium(including a storage device associated with a computing device or clientelectronic device) may be, for example, but is not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, device, or any suitable combination ofthe foregoing. More specific examples (a non-exhaustive list) of thecomputer-readable medium may include the following: an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a digital versatile disk (DVD), a static randomaccess memory (SRAM), a memory stick, a floppy disk, a mechanicallyencoded device such as punch-cards or raised structures in a groovehaving instructions recorded thereon, a media such as those supportingthe internet or an intranet, or a magnetic storage device. Note that thecomputer-usable or computer-readable medium could even be a suitablemedium upon which the program is stored, scanned, compiled, interpreted,or otherwise processed in a suitable manner, if necessary, and thenstored in a computer memory. In the context of the present disclosure, acomputer-usable or computer-readable, storage medium may be any tangiblemedium that can contain or store a program for use by or in connectionwith the instruction execution system, apparatus, or device.

In some implementations, a computer readable signal medium may include apropagated data signal with computer readable program code embodiedtherein, for example, in baseband or as part of a carrier wave. In someimplementations, such a propagated signal may take any of a variety offorms, including, but not limited to, electro-magnetic, optical, or anysuitable combination thereof. In some implementations, the computerreadable program code may be transmitted using any appropriate medium,including but not limited to the internet, wireline, optical fibercable, RF, etc. In some implementations, a computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that can communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device.

In some implementations, computer program code for carrying outoperations of the present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java®, Smalltalk, C++ or the like.Java® and all Java-based trademarks and logos are trademarks orregistered trademarks of Oracle and/or its affiliates. However, thecomputer program code for carrying out operations of the presentdisclosure may also be written in conventional procedural programminglanguages, such as the “C” programming language, PASCAL, or similarprogramming languages, as well as in scripting languages such asJavascript, PERL, or Python. The program code may execute entirely onthe user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough a local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theinternet using an Internet Service Provider). In some implementations,electronic circuitry including, for example, programmable logiccircuitry, field-programmable gate arrays (FPGAs) or other hardwareaccelerators, micro-controller units (MCUs), or programmable logicarrays (PLAs) may execute the computer readable programinstructions/code by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

In some implementations, the flowchart and block diagrams in the figuresillustrate the architecture, functionality, and operation of possibleimplementations of apparatus (systems), methods and computer programproducts according to various implementations of the present disclosure.Each block in the flowchart and/or block diagrams, and combinations ofblocks in the flowchart and/or block diagrams, may represent a module,segment, or portion of code, which comprises one or more executablecomputer program instructions for implementing the specified logicalfunction(s)/act(s). These computer program instructions may be providedto a processor of a general purpose computer, special purpose computer,or other programmable data processing apparatus to produce a machine,such that the computer program instructions, which may execute via theprocessor of the computer or other programmable data processingapparatus, create the ability to implement one or more of thefunctions/acts specified in the flowchart and/or block diagram block orblocks or combinations thereof. It should be noted that, in someimplementations, the functions noted in the block(s) may occur out ofthe order noted in the figures (or combined or omitted). For example,two blocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

In some implementations, these computer program instructions may also bestored in a computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks or combinations thereof

In some implementations, the computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed (not necessarilyin a particular order) on the computer or other programmable apparatusto produce a computer implemented process such that the instructionswhich execute on the computer or other programmable apparatus providesteps for implementing the functions/acts (not necessarily in aparticular order) specified in the flowchart and/or block diagram blockor blocks or combinations thereof

Referring now to the example implementation of FIG. 1, there is shownbucket process 10 that may reside on and may be executed by a computer(e.g., computer 12), which may be connected to a network (e.g., network14) (e.g., the internet or a local area network). Examples of computer12 (and/or one or more of the client electronic devices noted below) mayinclude, but are not limited to, a storage system (e.g., a NetworkAttached Storage (NAS) system, a Storage Area Network (SAN)), a personalcomputer(s), a laptop computer(s), mobile computing device(s), a servercomputer, a series of server computers, a mainframe computer(s), or acomputing cloud(s). As is known in the art, a SAN may include one ormore of the client electronic devices, including a RAID device and a NASsystem. In some implementations, each of the aforementioned may begenerally described as a computing device. In certain implementations, acomputing device may be a physical or virtual device. In manyimplementations, a computing device may be any device capable ofperforming operations, such as a dedicated processor, a portion of aprocessor, a virtual processor, a portion of a virtual processor,portion of a virtual device, or a virtual device. In someimplementations, a processor may be a physical processor or a virtualprocessor. In some implementations, a virtual processor may correspondto one or more parts of one or more physical processors. In someimplementations, the instructions/logic may be distributed and executedacross one or more processors, virtual or physical, to execute theinstructions/logic. Computer 12 may execute an operating system, forexample, but not limited to, Microsoft® Windows®; Mac® OS X®; Red Hat®Linux®, Windows® Mobile, Chrome OS, Blackberry OS, Fire OS, or a customoperating system. (Microsoft and Windows are registered trademarks ofMicrosoft Corporation in the United States, other countries or both; Macand OS X are registered trademarks of Apple Inc. in the United States,other countries or both; Red Hat is a registered trademark of Red HatCorporation in the United States, other countries or both; and Linux isa registered trademark of Linus Torvalds in the United States, othercountries or both).

In some implementations, as will be discussed below in greater detail, abucket process, such as bucket process 10 of FIG. 1, may store data in abucket of a plurality of buckets. A spare bucket may be reserved in theplurality of buckets. A copy of the data may be stored in the sparebucket. A pointer to the data in the bucket and a pointer to the copy ofthe data in the spare bucket may be updated based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.

In some implementations, the instruction sets and subroutines of bucketprocess 10, which may be stored on storage device, such as storagedevice 16, coupled to computer 12, may be executed by one or moreprocessors and one or more memory architectures included within computer12. In some implementations, storage device 16 may include but is notlimited to: a hard disk drive; all forms of flash memory storagedevices; a tape drive; an optical drive; a RAID array (or other array);a random access memory (RAM); a read-only memory (ROM); or combinationthereof. In some implementations, storage device 16 may be organized asan extent, an extent pool, a RAID extent (e.g., an example 4D+1P R5,where the RAID extent may include, e.g., five storage device extentsthat may be allocated from, e.g., five different storage devices), amapped RAID (e.g., a collection of RAID extents), or combinationthereof.

In some implementations, network 14 may be connected to one or moresecondary networks (e.g., network 18), examples of which may include butare not limited to: a local area network; a wide area network or othertelecommunications network facility; or an intranet, for example. Thephrase “telecommunications network facility,” as used herein, may referto a facility configured to transmit, and/or receive transmissionsto/from one or more mobile client electronic devices (e.g., cellphones,etc.) as well as many others.

In some implementations, computer 12 may include a data store, such as adatabase (e.g., relational database, object-oriented database,triplestore database, etc.) and may be located within any suitablememory location, such as storage device 16 coupled to computer 12. Insome implementations, data, metadata, information, etc. describedthroughout the present disclosure may be stored in the data store. Insome implementations, computer 12 may utilize any known databasemanagement system such as, but not limited to, DB2, in order to providemulti-user access to one or more databases, such as the above notedrelational database. In some implementations, the data store may also bea custom database, such as, for example, a flat file database or an XMLdatabase. In some implementations, any other form(s) of a data storagestructure and/or organization may also be used. In some implementations,bucket process 10 may be a component of the data store, a standaloneapplication that interfaces with the above noted data store and/or anapplet/application that is accessed via client applications 22, 24, 26,28. In some implementations, the above noted data store may be, in wholeor in part, distributed in a cloud computing topology. In this way,computer 12 and storage device 16 may refer to multiple devices, whichmay also be distributed throughout the network.

In some implementations, computer 12 may execute a storage managementapplication (e.g., storage management application 21), examples of whichmay include, but are not limited to, e.g., a storage system application,a cloud computing application, a data synchronization application, adata migration application, a garbage collection application, or otherapplication that allows for the implementation and/or management of datain a clustered (or non-clustered) environment (or the like). In someimplementations, bucket process 10 and/or storage management application21 may be accessed via one or more of client applications 22, 24, 26,28. In some implementations, bucket process 10 may be a standaloneapplication, or may be an applet/application/script/extension that mayinteract with and/or be executed within storage management application21, a component of storage management application 21, and/or one or moreof client applications 22, 24, 26, 28. In some implementations, storagemanagement application 21 may be a standalone application, or may be anapplet/application/script/extension that may interact with and/or beexecuted within bucket process 10, a component of bucket process 10,and/or one or more of client applications 22, 24, 26, 28. In someimplementations, one or more of client applications 22, 24, 26, 28 maybe a standalone application, or may be anapplet/application/script/extension that may interact with and/or beexecuted within and/or be a component of bucket process 10 and/orstorage management application 21. Examples of client applications 22,24, 26, 28 may include, but are not limited to, e.g., a storage systemapplication, a cloud computing application, a data synchronizationapplication, a data migration application, a garbage collectionapplication, or other application that allows for the implementationand/or management of data in a clustered (or non-clustered) environment(or the like), a standard and/or mobile web browser, an emailapplication (e.g., an email client application), a textual and/or agraphical user interface, a customized web browser, a plugin, anApplication Programming Interface (API), or a custom application. Theinstruction sets and subroutines of client applications 22, 24, 26, 28,which may be stored on storage devices 30, 32, 34, 36, coupled to clientelectronic devices 38, 40, 42, 44, may be executed by one or moreprocessors and one or more memory architectures incorporated into clientelectronic devices 38, 40, 42, 44.

In some implementations, one or more of storage devices 30, 32, 34, 36,may include but are not limited to: hard disk drives; flash drives, tapedrives; optical drives; RAID arrays; random access memories (RAM); andread-only memories (ROM). Examples of client electronic devices 38, 40,42, 44 (and/or computer 12) may include, but are not limited to, apersonal computer (e.g., client electronic device 38), a laptop computer(e.g., client electronic device 40), a smart/data-enabled, cellularphone (e.g., client electronic device 42), a notebook computer (e.g.,client electronic device 44), a tablet, a server, a television, a smarttelevision, a smart speaker, an Internet of Things (IoT) device, a media(e.g., video, photo, etc.) capturing device, and a dedicated networkdevice. Client electronic devices 38, 40, 42, 44 may each execute anoperating system, examples of which may include but are not limited to,Android™, Apple® iOS®, Mac® OS X®; Red Hat® Linux®, Windows® Mobile,Chrome OS, Blackberry OS, Fire OS, or a custom operating system.

In some implementations, one or more of client applications 22, 24, 26,28 may be configured to effectuate some or all of the functionality ofbucket process 10 (and vice versa). Accordingly, in someimplementations, bucket process 10 may be a purely server-sideapplication, a purely client-side application, or a hybridserver-side/client-side application that is cooperatively executed byone or more of client applications 22, 24, 26, 28 and/or bucket process10.

In some implementations, one or more of client applications 22, 24, 26,28 may be configured to effectuate some or all of the functionality ofstorage management application 21 (and vice versa). Accordingly, in someimplementations, storage management application 21 may be a purelyserver-side application, a purely client-side application, or a hybridserver-side/client-side application that is cooperatively executed byone or more of client applications 22, 24, 26, 28 and/or storagemanagement application 21. As one or more of client applications 22, 24,26, 28, bucket process 10, and storage management application 21, takensingly or in any combination, may effectuate some or all of the samefunctionality, any description of effectuating such functionality viaone or more of client applications 22, 24, 26, 28, bucket process 10,storage management application 21, or combination thereof, and anydescribed interaction(s) between one or more of client applications 22,24, 26, 28, bucket process 10, storage management application 21, orcombination thereof to effectuate such functionality, should be taken asan example only and not to limit the scope of the disclosure.

In some implementations, one or more of users 46, 48, 50, 52 may accesscomputer 12 and bucket process 10 (e.g., using one or more of clientelectronic devices 38, 40, 42, 44) directly through network 14 orthrough secondary network 18. Further, computer 12 may be connected tonetwork 14 through secondary network 18, as illustrated with phantomlink line 54. Bucket process 10 may include one or more user interfaces,such as browsers and textual or graphical user interfaces, through whichusers 46, 48, 50, 52 may access bucket process 10.

In some implementations, the various client electronic devices may bedirectly or indirectly coupled to network 14 (or network 18). Forexample, client electronic device 38 is shown directly coupled tonetwork 14 via a hardwired network connection. Further, clientelectronic device 44 is shown directly coupled to network 18 via ahardwired network connection. Client electronic device 40 is shownwirelessly coupled to network 14 via wireless communication channel 56established between client electronic device 40 and wireless accesspoint (i.e., WAP) 58, which is shown directly coupled to network 14. WAP58 may be, for example, an IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, Wi-Fi®, RFID, and/or Bluetooth™ (including Bluetooth™ LowEnergy) device that is capable of establishing wireless communicationchannel 56 between client electronic device 40 and WAP 58. Clientelectronic device 42 is shown wirelessly coupled to network 14 viawireless communication channel 60 established between client electronicdevice 42 and cellular network/bridge 62, which is shown by exampledirectly coupled to network 14.

In some implementations, some or all of the IEEE 802.11x specificationsmay use Ethernet protocol and carrier sense multiple access withcollision avoidance (i.e., CSMA/CA) for path sharing. The various802.11x specifications may use phase-shift keying (i.e., PSK) modulationor complementary code keying (i.e., CCK) modulation, for example.Bluetooth™ (including Bluetooth™ Low Energy) is a telecommunicationsindustry specification that allows, e.g., mobile phones, computers,smart phones, and other electronic devices to be interconnected using ashort-range wireless connection. Other forms of interconnection (e.g.,Near Field Communication (NFC)) may also be used.

In some implementations, various I/O requests (e.g., I/O request 15) maybe sent from, e.g., client applications 22, 24, 26, 28 to, e.g.,computer 12. Examples of I/O request 15 may include but are not limitedto, data write requests (e.g., a request that content be written tocomputer 12) and data read requests (e.g., a request that content beread from computer 12).

Data Storage System

Referring also to the example implementation of FIGS. 2-3 (e.g., wherecomputer 12 may be configured as a data storage system), computer 12 mayinclude storage processor 100 and a plurality of storage targets (e.g.,storage targets 102, 104, 106, 108, 110). In some implementations,storage targets 102, 104, 106, 108, 110 may include any of theabove-noted storage devices. In some implementations, storage targets102, 104, 106, 108, 110 may be configured to provide various levels ofperformance and/or high availability. For example, storage targets 102,104, 106, 108, 110 may be configured to form a non-fully-duplicativefault-tolerant data storage system (such as a non-fully-duplicative RAIDdata storage system), examples of which may include but are not limitedto: RAID 3 arrays, RAID 4 arrays, RAID 5 arrays, and/or RAID 6 arrays.It will be appreciated that various other types of RAID arrays may beused without departing from the scope of the present disclosure.

While in this particular example, computer 12 is shown to include fivestorage targets (e.g., storage targets 102, 104, 106, 108, 110), this isfor example purposes only and is not intended limit the presentdisclosure. For instance, the actual number of storage targets may beincreased or decreased depending upon, e.g., the level ofredundancy/performance/capacity required.

Further, the storage targets (e.g., storage targets 102, 104, 106, 108,110) included with computer 12 may be configured to form a plurality ofdiscrete storage arrays. For instance, and assuming for example purposesonly that computer 12 includes, e.g., ten discrete storage targets, afirst five targets (of the ten storage targets) may be configured toform a first RAID array and a second five targets (of the ten storagetargets) may be configured to form a second RAID array.

In some implementations, one or more of storage targets 102, 104, 106,108, 110 may be configured to store coded data (e.g., via storagemanagement process 21), wherein such coded data may allow for theregeneration of data lost/corrupted on one or more of storage targets102, 104, 106, 108, 110. Examples of such coded data may include but isnot limited to parity data and Reed-Solomon data. Such coded data may bedistributed across all of storage targets 102, 104, 106, 108, 110 or maybe stored within a specific storage target.

Examples of storage targets 102, 104, 106, 108, 110 may include one ormore data arrays, wherein a combination of storage targets 102, 104,106, 108, 110 (and any processing/control systems associated withstorage management application 21) may form data array 112.

The manner in which computer 12 is implemented may vary depending upone.g., the level of redundancy/performance/capacity required. Forexample, computer 12 may be configured as a SAN (i.e., a Storage AreaNetwork), in which storage processor 100 may be, e.g., a dedicatedcomputing system and each of storage targets 102, 104, 106, 108, 110 maybe a RAID device. An example of storage processor 100 may include but isnot limited to a VPLEX™ system offered by Dell EMC™ of Hopkinton, Mass.

In the example where computer 12 is configured as a SAN, the variouscomponents of computer 12 (e.g., storage processor 100, and storagetargets 102, 104, 106, 108, 110) may be coupled using networkinfrastructure 114, examples of which may include but are not limited toan Ethernet (e.g., Layer 2 or Layer 3) network, a fiber channel network,an InfiniB and network, or any other circuit switched/packet switchednetwork.

As discussed above, various I/O requests (e.g., I/O request 15) may begenerated. For example, these I/O requests may be sent from, e.g.,client applications 22, 24, 26, 28 to, e.g., computer 12.Additionally/alternatively (e.g., when storage processor 100 isconfigured as an application server or otherwise), these I/O requestsmay be internally generated within storage processor 100 (e.g., viastorage management process 21). Examples of I/O request 15 may includebut are not limited to data write request 116 (e.g., a request thatcontent 118 be written to computer 12) and data read request 120 (e.g.,a request that content 118 be read from computer 12).

In some implementations, during operation of storage processor 100,content 118 to be written to computer 12 may be received and/orprocessed by storage processor 100 (e.g., via storage management process21). Additionally/alternatively (e.g., when storage processor 100 isconfigured as an application server or otherwise), content 118 to bewritten to computer 12 may be internally generated by storage processor100 (e.g., via storage management process 21).

As discussed above, the instruction sets and subroutines of storagemanagement application 21, which may be stored on storage device 16included within computer 12, may be executed by one or more processorsand one or more memory architectures included with computer 12.Accordingly, in addition to being executed on storage processor 100,some or all of the instruction sets and subroutines of storagemanagement application 21 (and/or bucket process 10) may be executed byone or more processors and one or more memory architectures includedwith data array 112.

In some implementations, storage processor 100 may include front endcache memory system 122. Examples of front end cache memory system 122may include but are not limited to a volatile, solid-state, cache memorysystem (e.g., a dynamic RAM cache memory system), a non-volatile,solid-state, cache memory system (e.g., a flash-based, cache memorysystem), and/or any of the above-noted storage devices.

In some implementations, storage processor 100 may initially storecontent 118 within front end cache memory system 122. Depending upon themanner in which front end cache memory system 122 is configured, storageprocessor 100 (e.g., via storage management process 21) may immediatelywrite content 118 to data array 112 (e.g., if front end cache memorysystem 122 is configured as a write-through cache) or may subsequentlywrite content 118 to data array 112 (e.g., if front end cache memorysystem 122 is configured as a write-back cache).

In some implementations, one or more of storage targets 102, 104, 106,108, 110 may include a backend cache memory system. Examples of thebackend cache memory system may include but are not limited to avolatile, solid-state, cache memory system (e.g., a dynamic RAM cachememory system), a non-volatile, solid-state, cache memory system (e.g.,a flash-based, cache memory system), and/or any of the above-notedstorage devices.

Storage Targets

As discussed above, one or more of storage targets 102, 104, 106, 108,110 may be a RAID device. For instance, and referring also to FIG. 3,there is shown example target 150, wherein target 150 may be one exampleimplementation of a RAID implementation of, e.g., storage target 102,storage target 104, storage target 106, storage target 108, and/orstorage target 110. An example of target 150 may include but is notlimited to a VNX™ system offered by Dell EMC™ of Hopkinton, Mass.Examples of storage devices 154, 156, 158, 160, 162 may include one ormore electro-mechanical hard disk drives, one or more solid-state/flashdevices, and/or any of the above-noted storage devices. It will beappreciated that while the term “disk” or “drive” may be usedthroughout, these may refer to and be used interchangeably with anytypes of appropriate storage devices as the context and functionality ofthe storage device permits.

In some implementations, target 150 may include storage processor 152and a plurality of storage devices (e.g., storage devices 154, 156, 158,160, 162). Storage devices 154, 156, 158, 160, 162 may be configured toprovide various levels of performance and/or high availability (e.g.,via storage management process 21). For example, one or more of storagedevices 154, 156, 158, 160, 162 (or any of the above-noted storagedevices) may be configured as a RAID 0 array, in which data is stripedacross storage devices. By striping data across a plurality of storagedevices, improved performance may be realized. However, RAID 0 arraysmay not provide a level of high availability. Accordingly, one or moreof storage devices 154, 156, 158, 160, 162 (or any of the above-notedstorage devices) may be configured as a RAID 1 array, in which data ismirrored between storage devices. By mirroring data between storagedevices, a level of high availability may be achieved as multiple copiesof the data may be stored within storage devices 154, 156, 158, 160,162.

While storage devices 154, 156, 158, 160, 162 are discussed above asbeing configured in a RAID 0 or RAID 1 array, this is for examplepurposes only and not intended to limit the present disclosure, as otherconfigurations are possible. For example, storage devices 154, 156, 158,160, 162 may be configured as a RAID 3, RAID 4, RAID 5 or RAID 6 array.

While in this particular example, target 150 is shown to include fivestorage devices (e.g., storage devices 154, 156, 158, 160, 162), this isfor example purposes only and not intended to limit the presentdisclosure. For instance, the actual number of storage devices may beincreased or decreased depending upon, e.g., the level ofredundancy/performance/capacity required.

In some implementations, one or more of storage devices 154, 156, 158,160, 162 may be configured to store (e.g., via storage managementprocess 21) coded data, wherein such coded data may allow for theregeneration of data lost/corrupted on one or more of storage devices154, 156, 158, 160, 162. Examples of such coded data may include but arenot limited to parity data and Reed-Solomon data. Such coded data may bedistributed across all of storage devices 154, 156, 158, 160, 162 or maybe stored within a specific storage device.

The manner in which target 150 is implemented may vary depending upone.g., the level of redundancy/performance/capacity required. Forexample, target 150 may be a RAID device in which storage processor 152is a RAID controller card and storage devices 154, 156, 158, 160, 162are individual “hot-swappable” hard disk drives. Another example oftarget 150 may be a RAID system, examples of which may include but arenot limited to an NAS (i.e., Network Attached Storage) device or a SAN(i.e., Storage Area Network).

In some implementations, storage target 150 may execute all or a portionof storage management application 21. The instruction sets andsubroutines of storage management application 21, which may be stored ona storage device (e.g., storage device 164) coupled to storage processor152, may be executed by one or more processors and one or more memoryarchitectures included with storage processor 152. Storage device 164may include but is not limited to any of the above-noted storagedevices.

As discussed above, computer 12 may be configured as a SAN, whereinstorage processor 100 may be a dedicated computing system and each ofstorage targets 102, 104, 106, 108, 110 may be a RAID device.Accordingly, when storage processor 100 processes data requests 116,120, storage processor 100 (e.g., via storage management process 21) mayprovide the appropriate requests/content (e.g., write request 166,content 168 and read request 170) to, e.g., storage target 150 (which isrepresentative of storage targets 102, 104, 106, 108 and/or 110).

In some implementations, during operation of storage processor 152,content 168 to be written to target 150 may be processed by storageprocessor 152 (e.g., via storage management process 21). Storageprocessor 152 may include cache memory system 172. Examples of cachememory system 172 may include but are not limited to a volatile,solid-state, cache memory system (e.g., a dynamic RAM cache memorysystem) and/or a non-volatile, solid-state, cache memory system (e.g., aflash-based, cache memory system). During operation of storage processor152, content 168 to be written to target 150 may be received by storageprocessor 152 (e.g., via storage management process 21) and initiallystored (e.g., via storage management process 21) within front end cachememory system 172.

A hash table is generally a data structure which implements anassociative array abstract data type, a structure that may map keys tovalues. It uses a hash function to compute from a given key an indexinto an array of buckets, from which the desired value may be found. Abasic requirement is that the hash function should provide a uniformdistribution of hash values over the table size. We consider hashcollisions resolution (where the hash function generates the same indexfor more than one key) by chaining entries with the same bucket. A fixedsize hash table is a table with fixed number of bucket (N), each one ofa fixed maximal number of entries (M). Example: hash table with1,000,000 buckets, each one with maximal 256 entries rounded to theclosest native block size, e.g., 4 KB.

Hardening a fixed size hash table includes saving this data structureinto non-volatile memory with a read-modify-write update operation.Assume the system is hardening the hash table into a dedicated logicaladdress space over persistent media (named as “tier”), i.e.,:

-   Bucket #0 resides at logical offset 0,-   bucket #1 resides at offset bucket size, . . . ,-   bucket #i resides at offset bucket size*(i−1)-   bucket size:=4 KB (as in the example).

The above does not guarantee write operation atomicity, i.e.,: if duringwrite operation the system restarts or powers off, the logical blockwritten to the tier might end with inconsistent data. Such unreliabletier is common in storage systems where the logical blocks written overa complex and non-native device media type, e.g.,: RAID over multipledisks or logical block that is larger than the device native block size.Due to this kind of issue, to guarantee consistent data while workingwith such tier, one must assure atomicity by its applicative logic.In-place lockless updates of a bucket over an unreliable tier may resultwith inconsistent data as the read-modify write operation atomicity isnot guaranteed. In general, many storage systems solve this issue byexcessive transactional journal implementations, which may result in anadditional write overhead of the data to be updated, that will be usedonly upon failure.

Thus, as will be discussed below, the present disclosure may enableupdates to a fixed size hash table in a read-modify-write fashion whichis lockless and highly scalable, while efficient in terms of metadatarepresentation and CPU. The present disclosure may include anapplicative algorithm of assuring read-modify-write atomicity duringhardening a fixed size hash table, and may include a space-efficientmapping kept in non-volatile memory, as well as an extra slot innon-volatile memory, which together will consist of the transactionneeded for creating an atomic read-modify-write operation. Unlike otherstorage systems, as it is a lockless and totally independentimplementation, the system may be easily scaled and enable multiplesimultaneous updates.

The Bucket Process

As discussed above and referring also at least to the exampleimplementations of FIG. 4, bucket process 10 may store 400 data in abucket of a plurality of buckets. Bucket process 10 may reserve 402 aspare bucket in the plurality of buckets. Bucket process 10 may store404 a copy of the data in the spare bucket. Bucket process 10 may update406 a pointer to the data in the bucket and a pointer to the copy of thedata in the spare bucket based upon, at least in part, storing the datain the bucket and storing the copy of the data in the spare bucket.

In some implementations, bucket process 10 may store 400 data in abucket of a plurality of buckets. For example, the logical tier may bein the following structure:

Size:=(#bucket*bucket_size)+1 (“spare”)

In some implementations, buckets may be stored in a cyclic andconsecutive manner over the n+1 slots.

In some implementations, bucket process 10 may reserve 402 a sparebucket in the plurality of buckets, and the spare bucket may be a nextslot from the bucket. For example, along with the n buckets, bucketprocess 10 may reserve 402 one slot as a spare_bucket, which representsthe next slot to be written. In the example, the system does not assumeanything regarding data in the spare slot (and therefore does not everread it).

Non-limiting examples of a valid 5 buckets layout during system durationis as follows:

-   [bucket_3][bucket_4][spare_bucket][bucket_0][bucket_1][bucket_2]-   [bucket_0][bucket_1][bucket_2][spare_bucket][bucket_3][bucket_4]

In some implementations, bucket process 10 may use two metadata fields(e.g., pointers) as follows:

-   Head—states the index in which bucket_0 is located.-   Spare—states the index in which spare_bucket is located.

In some implementations, these fields will be kept in non-volatilememory. Since head states the index of the first bucket, and the sparestates the next slot to be written (and does not present data which isnecessarily valid), as well as the fact that buckets are stored in aconsecutive manner, reading bucket i is performed by skipping i slotsfrom the slot stated by head in a cyclic manner and skipping anotherslot if the slot stated by spare was reached at any point (also in acyclic manner).

Non-limiting examples of reading are as follows:

-   Reading bucket_3:-   [A][B][C][D][E][F]-   Head=3-   Spare=2

From the metadata fields, the following is revealed:

-   [A][B][spare_bucket][bucket_0][E][F]-   Bucket 3 is locates is at slot 0 (A).-   Reading bucket 3:-   [A][B][C][D][E][F]-   Head=4-   Spare=1-   From the metadata fields, the following is revealed:-   [A][spare_bucket][C][D][bucket_0][F]-   Bucket_3 is locates at slot 2 (C).

In some implementations, bucket process 10 may store 404 a copy of thedata in the spare bucket, and may update 406 a pointer to the data inthe bucket and a pointer to the copy of the data in the spare bucketbased upon, at least in part, storing the data in the bucket and storingthe copy of the data in the spare bucket, where updating the pointer tothe copy of the data in the spare bucket may include pointing 408 to thebucket storing the data. For example, updating bucket i may be performedas follows:

-   Read bucket i from slot s in tier-   Modify bucket-   Write (store) bucket i into spare_bucket location-   If i==0: Update head to be spare.-   Update spare location to be s (previous bucket i location)

The “update head to be spare” and “update spare location to be s” mustbe performed atomically.

Example of several bucket updates are as follows:

-   Original state:    -   [bkt_3][bkt_4][spare_bkt][bkt_0][bkt_1][bkt_2]    -   Head=3    -   Spare=2    -   Update bucket_0:    -   [bkt_3][bkt_4][updated_bkt_0][spare][bkt_1][bkt_2]    -   Head=2    -   Spare=3-   Update bucket_1:    -   [bkt_3][bkt_4][updated_bkt_0][updated_bkt_1][spare][bkt_2]    -   Head=2    -   Spare=4

Performing the read-modify write operation in this manner guaranteesatomicity, since bucket process 10 never writes bucket in-place, bucketprocess 10 either has the old or updated bucket copy. This means that atany point, if the system were to restart, the data would be completelyconsistent.

As presented, at no point there is no bucket lock used in the processand there is achieved uninterrupted read while bucket process 10simultaneously updates the same bucket. The system achieves atransaction which protects the read-modify operation at a low cost: 2members stating head and spare on non-volatile memory. Compare totraditional bucket journaling (e.g., N×4K) which is a redundantadditional full-page update (typically used only in failure). The spareslot is generally insignificant as well, assuming the logical tier willconsist of many buckets (just 1 spare regardless of number of buckets).

In some implementations, the plurality of buckets may be updated 410 ina consecutive-cyclic manner. For example, updates may be in bucketconsecutive order, since bucket updates the writes to the spare bucket,and the spare bucket location changes to the previous slot of the bucketthat is updated. As described above, during bucket read we assume thatbuckets are stored in a cyclic and consecutive manner. Therefore,writing in non-consecutive order will result in breaking the invariantof the last point. For instance:

-   Original state:    -   [bkt_3][bkt_4][spare_bkt][bkt_0][bkt_1][bkt_2]    -   Head=3    -   Spare=2-   Update bucket 0:    -   [bkt_3][bkt_4][updated_bkt_0][spare][bkt_1][bkt_2]    -   Head=2    -   Spare=3-   Update bucket_2:    -   [bkt_3][bkt_4][updated_bkt_0][updated_bkt_2][bkt_1][spare]    -   Head=2    -   Spare=5

If the system were to read buckets 1-2 using the algorithm describedabove, the wrong bucket would be read. As such, bucket process 10 mayupdate the buckets in a consecutive-cyclic (e.g., ascending) manner,meaning the buckets are updated in the following example:

-   0, 1, 2 . . . , i+1, . . . ,n−1, 0, 1 . . .

As mentioned above, the buckets being hardened represent buckets of auniformly distributed hash table, meaning updates will be distributedevenly on average. This means that if the tier has n buckets and kupdates, on average each bucket will have k/n new updates. Therefore, ifbucket i and bucket j have no pending updates, and there were k newupdates for a complete hash table, it may be assumed that buckets i,jhave k/n updates each. If bucket i were updated by the hardeningalgorithm, and afterward there were x additional updated to the system,it may be known that on average bucket i has x/n pending updates, whilebucket j has (k+x)/n new updates. Therefore, there is no need inupdating bucket i again, prior to the update of bucket j. This statementit true to all other n−2 buckets. This means that prior to bucket ibeing updated again, all other buckets must be updated. Accordingly,this is why it is possible (and beneficial) to take a consecutive bucketupdate approach.

The plurality of buckets may be divided 412 between a fixed number ofdomains, wherein each domain of the fixed number of domains may be aninstance of an independent logical tier, and wherein each domain of thefixed number of domains may include its own header and spare metadatamember. For instance, the above-noted update algorithm may suffer fromscaling issues, meaning it does not necessarily support two bucketsbeing updated at the same time, due to the fact that it uses a singlespare slot for the next bucket update. However, scaling may still beachieved by introducing domains.

For example, the n buckets may be divided equally between a fixed number(d) of domains. Each domain may consist of a collection of n/dconsecutive buckets. Each domain may implement the logical tierdescribed above and may be of size ((n/d)+1)*bucket_size. This meansthat each domain may in fact be an instance of an independent logicaltier, which stores a group of buckets in a consecutive and cyclicmanner, and therefore will have its own header and spare metadatamembers. Each domain may be updated as an independent unit, without anyregard to other domains. For example:

-   2 domains, 6 buckets.-   Domain 0: [bkt_0] [bkt_1] [bkt_2] [spare]    -   Head: 0; Spare: 3.-   Domain 1: [bkt_3] [bkt_4] [bkt_5] [spare]    -   Head: 0; Spare: 3

Whereas domain 1 marks bkt_3 as its first bucket (as stated in head).

The fixed number of domains is the scaling upper-bound of the tier, andtherefore it is possible to update as many as d buckets at the same time(since each domain can serve just one update at the same time). Bucketupdates may be at a cyclic consecutive manner in a domain, and may be ina round-robin fashion between domains. For example,

-   2 domains, 6 buckets.-   Original state:    -   Domain 0: [bkt_0][bkt_1][bkt_2][spare]    -   Head: 0; Spare: 3.    -   Domain 1: [bkt_3][bkt_4][bkt_5][spare]

Head: 0; Spare: 3

-   -   Update bucket 0:    -   Domain 0: [spare][bkt_1][bkt_2][updated_bkt_0]    -   Head: 3; Spare: 0.    -   Domain 1: [bkt_3][bkt_4][bkt_5][spare]    -   Head: 0; Spare: 3    -   Update buckets 1,3:    -   Domain 0: [updated_bkt_1][spare][bkt_2][updated_bkt_0]    -   Head: 3; Spare: 1.    -   Domain 1: [spare][bkt_4][bkt_5][updated_bkt_3]    -   Head: 3; Spare: 0    -   Update bucket 4:    -   Domain 0: [updated_bkt 1][bkt_2][bkt_2][updated_bkt_0]    -   Head: 3; Spare: 1.    -   Domain 1: [updated_bkt_4][spare][bkt_5][updated_bkt_3]    -   Head: 3; Spare: 4.

The terminology used herein is for the purpose of describing particularimplementations only and is not intended to be limiting of thedisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. As used herein, the language “at least one of A, B,and C” (and the like) should be interpreted as covering only A, only B,only C, or any combination of the three, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps (notnecessarily in a particular order), operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps (not necessarily in a particular order),operations, elements, components, and/or groups thereof

The corresponding structures, materials, acts, and equivalents (e.g., ofall means or step plus function elements) that may be in the claimsbelow are intended to include any structure, material, or act forperforming the function in combination with other claimed elements asspecifically claimed. The description of the present disclosure has beenpresented for purposes of illustration and description, but is notintended to be exhaustive or limited to the disclosure in the formdisclosed. Many modifications, variations, substitutions, and anycombinations thereof will be apparent to those of ordinary skill in theart without departing from the scope and spirit of the disclosure. Theimplementation(s) were chosen and described in order to explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various implementation(s) with various modifications and/or anycombinations of implementation(s) as are suited to the particular usecontemplated.

Having thus described the disclosure of the present application indetail and by reference to implementation(s) thereof, it will beapparent that modifications, variations, and any combinations ofimplementation(s) (including any modifications, variations,substitutions, and combinations thereof) are possible without departingfrom the scope of the disclosure defined in the appended claims.

What is claimed is:
 1. A computer-implemented method comprising: storingdata in a bucket of a plurality of buckets; reserving a spare bucket inthe plurality of buckets; storing a copy of the data in the sparebucket; and updating a pointer to the data in the bucket and a pointerto the copy of the data in the spare bucket based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.
 2. The computer-implemented method of claim 1 whereinthe spare bucket is a next slot from the bucket.
 3. Thecomputer-implemented method of claim 1 wherein updating the pointer tothe copy of the data in the spare bucket includes pointing to the bucketstoring the data.
 4. The computer-implemented method of claim 1 furthercomprising updating the plurality of buckets in a consecutive-cyclicmanner.
 5. The computer-implemented method of claim 1 further comprisingdividing the plurality of buckets between a fixed number of domains. 6.The computer-implemented method of claim 5 wherein each domain of thefixed number of domains is an instance of an independent logical tier.7. The computer-implemented method of claim 5 wherein each domain of thefixed number of domains includes its own header and spare metadatamember.
 8. A computer program product residing on a computer readablestorage medium having a plurality of instructions stored thereon which,when executed across one or more processors, causes at least a portionof the one or more processors to perform operations comprising: storingdata in a bucket of a plurality of buckets; reserving a spare bucket inthe plurality of buckets; storing a copy of the data in the sparebucket; and updating a pointer to the data in the bucket and a pointerto the copy of the data in the spare bucket based upon, at least inpart, storing the data in the bucket and storing the copy of the data inthe spare bucket.
 9. The computer program product of claim 8 wherein thespare bucket is a next slot from the bucket.
 10. The computer programproduct of claim 8 wherein updating the pointer to the copy of the datain the spare bucket includes pointing to the bucket storing the data.11. The computer program product of claim 8 wherein the operationsfurther comprise updating the plurality of buckets in aconsecutive-cyclic manner.
 12. The computer program product of claim 8wherein the operations further comprise dividing the plurality ofbuckets between a fixed number of domains.
 13. The computer programproduct of claim 12 wherein each domain of the fixed number of domainsis an instance of an independent logical tier.
 14. The computer programproduct of claim 12 wherein each domain of the fixed number of domainsincludes its own header and spare metadata member.
 15. A computingsystem including one or more processors and one or more memoriesconfigured to perform operations comprising: storing data in a bucket ofa plurality of buckets; reserving a spare bucket in the plurality ofbuckets; storing a copy of the data in the spare bucket; and updating apointer to the data in the bucket and a pointer to the copy of the datain the spare bucket based upon, at least in part, storing the data inthe bucket and storing the copy of the data in the spare bucket.
 16. Thecomputing system of claim 8 wherein the spare bucket is a next slot fromthe bucket.
 17. The computing system of claim 8 wherein updating thepointer to the copy of the data in the spare bucket includes pointing tothe bucket storing the data.
 18. The computing system of claim 8 whereinthe operations further comprise updating the plurality of buckets in aconsecutive-cyclic manner.
 19. The computing system of claim 8 whereinthe operations further comprise dividing the plurality of bucketsbetween a fixed number of domains.
 20. The computing system of claim 19wherein each domain of the fixed number of domains is an instance of anindependent logical tier, and wherein each domain of the fixed number ofdomains includes its own header and spare metadata member.